1. Technical Field
The present disclosure relates to a signal amplification circuit using a chopper amplifier and a signal amplification determination circuit including the signal amplification circuit, to determine signal level of an input signal.
2. Related Art
Conventionally, in order to add various convenient functions such as a power-saving function to home electronics, various sensors, such as infrared sensors, image sensors, and temperature sensors, have been developed.
In order to amplify the signal from the sensor, for example, a complementary metal oxide semiconductor (CMOS)-type amplifier is used. Nevertheless, some types of sensors generate so small a signal that the sensor signal is buried in the 1/f noise generated by the CMOS-type amplifier and the quality is decreased. Accordingly, this tiny sensor signal is amplified by an amplification circuit using a chopper amplifier.
At the same time, with increasing demand for lower power consumption, the power supply voltage supplied to devices such as sensors is decreasing. However the CMOS analog switches typically used in the chopper amplifier may unnecessarily block intermediate voltage level signals when the chopper amplifier is operated at low voltage.
To enable operation at low voltage, JP-2008-067050-A discloses a capacitance feedback-type chopper amplification circuit, constituted by a switched operational amplifier and chopper modulation circuit formed in the CMOS circuit.
However, in this example, the capacitance feedback-type chopper amplification circuit cannot amplify low-frequency input signals because, when a low-frequency input signal is input to the chopper amplification circuit, the output signal of the chopper amplification circuit is attenuated by parasitic capacitance parasitic to the input terminal of the switched operational amplifier.